I don't understand why this isn't the Chase Kolpath series, rather than the Alex Benedict series, since while Alex is the guy in charge, it's Chase that the books are about. In any case, while just as friendly and readable as McDevitt's other books, Echo isn't the best of the series. Perhaps, as with the Priscilla Hutchins series, McDevitt has simply run out of steam towards the end.
Echo is a good mystery story in the tradition of the Benedict series, but it suffers from a couple of defects. First, it sets up what seems a token effort at Chase-Alex conflict, which brings a welcome uncertainty into the book, but which McDevitt never really commits to. Second, the book has Chase and especially Alex pursuing an investigation at a very high cost - so high that not only is it not really credible, but it succeeds at the difficult task of making our heroes a lot less likeable. The book doesn't really recover from that.It means that while I have the next book in the series, Firebird, on my shelf, I'm less excited to read it.
Finally, the final reveal and denouement don't really fulfill the promise of the early chapters. They could have been successful with a different lead in, but here, it's a bit of a disappointment.
If you're a serious fan of the Benedict series, by all means, buy this - you'll enjoy it, even if it's not your favorite in the series. If you're new to the series, go back to A Talent for War or Polaris and start there. If you've sort of enjoyed the series, but not loved it, skip this and go one to one of McDevitt's other excellent books - try Eternity Road or The Engines of God.